Fuses have been employed in semiconductor circuits to allow "programming" of the operation thereof after or toward the end of the processing operation. These fuses are used to program bits in registers, trim the values for resistive devices associated with various operations and also to allow selection/deselection of blocks of circuitry. In the latter, this is utilized most recently for redundant circuits.
In some semiconductor circuits, such as DRAMs, redundant circuitry is placed onto the chip and then the chip tested prior to packaging and even separating the die from the wafer. In this process, a determination is made as to which bits are the "faulty" bits and then these bits are replaced. This replacement is achieved by replacing a section of the memory, typically a column, with a redundant column. The programming is achieved such that the redundant column is not only replaced, but the address thereof is also associated with the decoded address of the faulty column. This is typically achieved through the use of fuses that are disposed in a "closed" or short-circuited mode during the processing step and then, after a determination is made as to a faulty column, the fuses are "blown". This process is typically facilitated with a laser that is used to "scribe" the fuse in the middle thereof, thus increasing the resistance thereof.
During the fabrication of a fuse, a length of conductive material, such as aluminum or tungsten is disposed on the substrate during processing of one of the metal layers. This is typically connected to other circuitry and other metal layers via contacts between layers. Thereafter, a layer of protective oxide is disposed over the fuse layer for protection thereof. This is typical with all layers on a semiconductor circuit during processing, this being a protective oxide to prevent damage to the underlying layers from the atmosphere due to such actions as corrosion, etc. Thereafter, the oxide layer can be decreased in thickness in the vicinity of the fuse, or the fuse can be at a high enough layer that the oxide is relatively thin. This will facilitate penetration of the oxide by the laser during programming of the fuse. However, once the fuse is programmed or "blown", both the oxide and the fuse are penetrated. This, therefore, exposes the ends of the fuse at the break to the atmosphere. If the fuse is made from a corrosive material, oxidation or various chemical reactions can occur that will travel along the fuse to other metal layers to which it is attached. This corrosion can therefore cause failures at a later time.